1. Field of the Invention
This invention relates to an electrophotographic belt member, a process for producing the electrophotographic belt member, and an electrophotographic apparatus, and more particularly to an electrophotographic belt member having a specific resin composition, a process for producing the electrophotographic belt member, and an electrophotographic apparatus having the electrophotographic belt member.
2. Related Background Art
With progress of full-color image formation by electrophotographic apparatus in recent years, there is a more and more increasing demand for electrophotographic belt members having electrical conductivity, such as an intermediate transfer belt (a belt used when, before toner images formed on an electrophotographic photosensitive member are transferred to a transfer medium such as paper, the toner images are once transferred onto an intermediate transfer belt and thereafter the toner images held on the intermediate transfer belt are transferred to the transfer medium to obtain images), a transfer-transport belt (a belt used when toner images formed on image-bearing members are transferred to a transfer medium such as paper and the transfer medium is transported), a photosensitive belt and a fixing belt; in particular, for the intermediate transfer belt and the transfer-transport belt.
Then, the electrophotographic belt member is required to have the following properties.    1) To have a good resistance to creep;    2) to have a good resistance to flexing;    3) to have a good uniformity in electrical resistance;    4) to have a high breakdown strength;    5) to less cause a change in belt peripheral length due to service environment;    6) to have a low cost; and so forth.
Conducting agents used to endow the electrophotographic belt member with electrical conductivity can roughly be grouped into two types, a conductive filler and an ion-conducting agent.
At present, in most electrophotographic belt members having been put into practical use, carbon black is used as a conducting agent. For example, belts disclosed in Japanese Patent Application Laid-open No. 5-200904 and Japanese Patent No. 2886505 also contain carbon black (conductive filler).
When, however, such a conductive filler is compounded, problems tend to occur such that an unstable state of dispersion (i.e., production scattering) of conductive fillers causes variations in electrical resistance and that any faulty dispersion (i.e., agglomeration) of conductive fillers causes an extreme lowering of breakdown strength.
On the other hand, when the ion-conducting agent is used, since a dispersion of the ion-conducting agent is remarkably good, there may occur no problem such as the production scattering of electrical resistance and the lowering of breakdown strength. However, since most ion-conducting agents may gradually ooze out (i.e., bleed out) to the film surface, there is a problem that the surface resistance changes or that the surface of the electrophotographic photosensitive member stress-cracks to cause faulty images.
To cope with such problems, Japanese Patent Application Laid-open No. 8-50419 and Japanese Patent Publication No. 8-7505 disclose belts containing polyether-ester amide, polyether ester or polyether amide as a chief conducting agent so that the belt may undergo any change in resistance due to bleeding and can have uniform resistance values.
Now, the present inventors produced as an experiment the belts disclosed in these publications to evaluation as electrophotographic belt members used in electrophotographic apparatus. As the result, the belts disclosed in these publications have proved to have problems that;    (1) the resistance to creep becomes poor to cause a change in belt peripheral length during repeated used, so that multi-color toner images can not superimposingly be transferred to the preset position (color aberration); and    (2) the belt peripheral length greatly changes depending on service environment, and hence the belt and a drive roller of the belt may slip in a high-temperature and high-humidity environment to worsen the color aberration, or the belt tension may increase so abnormally in a low-temperature and low-humidity environment that the belt drive torque may become higher, until the belt can no longer be driven.
The problem (1) is presumed to be due to the fact that the polyether-ester amide, polyether ester and polyether amide are all so soft as to cause a lowering of modulus in tension of a resin composition.
The problem (2) is also presumed to be due to the fact that the polyether-ester amide, polyether ester and polyether amide all have so high a coefficient of linear expansion and a water absorption as to cause a great change in belt peripheral length depending on service environment.
Accordingly, in order to solve such new problems, the present inventors have attempted to compound an insulating filler so as to prevent the resistance to creep from becoming poor and the belt peripheral length from changing depending on service environment.
As the result, the mere addition of an insulating filler alone has proved to cause problems that the belt obtained may have so high an electrical resistance as to cause faulty transfer and that the resistance to flexing of the belt may lower to make the belt have an extremely short lifetime.
Thus, any electrophotographic belt member that satisfies all the requirements stated above has not been devised, and it has been long-awaited to bring out such a belt.